[media] drivers/media/usb/ttusb-budget/dvb-ttusb-budget.c: remove unnecessary null test before usb_free_urb

Fix checkpatch warning:
WARNING: usb_free_urb(NULL) is safe this check is probably not required
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>